1. Field of the Invention
This invention relates to a method of moving a molten zone of material through a solid body of semiconductor material and, in particular, to the migration of a metal "wire" through material having a diamond cubic crystal structure and at least one surface of the body has a (100) planar crystal orientation.
2. Description of the Prior Art
W. G. Pfann describes in "Zone Melting", John Wiley and Sons, Inc., New York (1966), a thermal gradient zone melting process to produce various desirable material configurations in a body of semiconductor material. The process had previously been disclosed in his issued U.S. Pat. No. 2,813,048, based on his application filed June 24, 1954. In both instances, cavities are generally formed in the surface of the body and a piece of wire of the metal to be migrated is disposed in the cavity. However, the resulting structures were not desirable for semiconductor usage.
M. Blumenfeld, in U.S. Pat. No. 3,897,277, teaches alloying aluminum to the surface of a body of silicon semiconductor material in an attempt to maintain the registry of the pattern of metal deposits to be migrated. However, problems of registry of the metal still plague one's attempt to obtain the precise orientation necessary for an array of deep diodes suitable for making X-ray imaging devices.
Recently, T. R. Anthony and H. E. Cline, discovered that employing selected etching of the surface and preferred crystallographic orientation enabled one to employ thermal gradient zone melting processing to make semiconductor devices commercially. The improved process resulted in a large savings in energy required to process semiconductor materials and increased the yields of devices fabricated thereby. For further information, one is directed to the teachings of Anthony and Cline in their recently granted U.S. Pat. No. 3,904,442, and U.S. Pat. No. 3,979,230.
There are a variety of applications for the unique vertical-junction geometries made possible by thermal migration. However, in many cases for thermal migration to compete with the highly developed conventional planar technology, it is necessary to control the widths of the narrow doped regions. Photolithograph techniques were used to form the initial metal stripes that are subsequently melted and moved across the thin silicon wafer in a thermal gradient. A thermal gradient is established by either an electron beam or a tungsten filament. Both heat flow by radiation and thermal conduction are considered in the calculation of the thermal gradient. The optical absorption of silicon becomes important because of the partial infrared transparency of silicon. Wafers with a range of stripe dimensions are processed at different temperatures to determine the effect of wafer orientation, film thickness, stripe width, and heating method on thermomigration processing.
A problem occurs in matching the width of the doped recrystallized material to that of the deposited film width because the width of the liquid zone depends on the processing temperature.
It is therefore an object of this invention to provide a new and improved method for moving a molten zone within a solid body, or water, of semiconductor material which overcomes the deficiencies of the prior art.
Another object of the invention is to provide a method for predicting the dimensions of the stripe of metal needed to produce a predetermined width of recrystallized dope material.
Another object of the invention is to provide a new and improved method for producing a uniform selectively doped region of constant width.
Other objects of this invention will, in part, be obvious and will, in part, appear hereinafter.